The endocrine pancreas consists primarily of islet cells that synthesize and secrete the peptide hormone glucagon, insulin, somatostatin and pancreatic polypeptide. Insulin gene expression is restricted to pancreatic islet β-cells of the mammalian pancreas through control mechanisms mediated in part by specific transcription factors. In other cells the insulin, other pancreatic hormones and specific peptidases genes are trancriptionally silent. The homeodomain protein PDX-1 (Pancreatic and Duodenal Homeobox gene-1, also known as IDX-1, IPF-1, STF-1 or IUF-1) plays a central role in regulating pancreatic islet development and function. PDX-1 is either directly or indirectly involved in islet-cell-specific expression of various genes such as for example insulin, glucagon somatostatin, proinsulin convertase 1/3 (PC1/3), GLUT-2 and glucokinase. Additionally, PDX-1 mediates insulin gene transcription in response to glucose.